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Radial Engineering


Radial Space Heater 500 Series Tube Drive


The Radial Space Heater 500 will add harmonics to the signal path without unwanted distortion, noise or phase shift. To check the type of distortion being generated, there is no better indicator than the even-order harmonic distortion that is evident when looking at the FFT (Fast Fourier Transform) where a near-perfect cascade flows. Even-order harmonic distortion is pleasing to the ear and can really add some sheen to your mix when applied correctly!

    • Radial Space Heater 500 FEATURES:

      • Studio grade 12AX7 tube overdrive
      • 35, 70 & 140 volt Heat switch to set plate B+ voltage
      • Transformer coupled output for vintage tone
      • Variable HPF & LPF filters to focus distortion

      The Radial Space Heater 500™ is a studio-grade tube distortion for the 500 series format. Built to provide anything from subtle warmth to thick and heavy harmonic distortion, the Space Heater 500 is both useful and fun!

      Designed for use in the Radial Workhorse or any other 500 series rack, the Space Heater is built around a 12AX7 tube. First, a drive control lets you determine the amount of signal passing through the tube. Next, a 3-position heat switch allows you to apply 35, 70 or 140 volts at the plate to change how the tube reacts to the signal. At the low 35V setting the tube is starved for voltage which causes the tube to break up at a very low volume. The middle 70V setting is a great starting point and allows the tube to handle more level before breaking up to a moderate distortion. At 140 volts, maximum voltage is applied to the tube producing slight saturation and warmth. Sweepable high-pass and low-pass filters can be assigned 'pre or post' tube, allowing you to focus the tube effect on a particular frequency band or cause the tube to react in a different way. Finally, an output level control provides attenuation or boost through an oversized Jensen transformer specially selected for its big bottom end and vintage character.

      Enhancing a snare with a touch of distortion can increase presence without losing dynamic range. Blending in some overdrive to a bass track can add clarity without overpowering. Adding distortion to a vocal track can add character and sizzle to cut through the mix without over-compression. The Space Heater 500's amazing 'adjustability' allows it to be used as a subtle effect or as a high gain monster. And no matter your approach, it is sure to find its way on nearly everything you record!

      The Space Heater 500… to infinity and beyond!
    • Radial Space Heater 500 SPECIFICATIONS:


      Circuit type:

      Thermionic Gain stage with solid state input and output buffers

      Frequency response:

      20Hz - 20KHz ± 1dB

      Total harmonic distortion:

      Varies with Drive and Level settings

      Dynamic range:


      Input impedance – bypassed:


      Input impedance – active:


      Maximum input:


      Maximum gain:

      32dB@140V, 27dB @70V, 13dB @35V

      Clip level - output:


      Output impedance:


      Equivalent input noise:


      Noise floor:


      Intermodulation distortion:

      Varies with drive and level settings

      Common mode rejection ratio:


      Unity gain control position:

      Drive & level at about 11 o'clock



      Drive, Level, Hi-Cut filter, Lo-Cut filter


      "Heat", EQ Pre/Post, IN

      Switches - rear panel:

      Heater polarity selection

      Filter slopes:


      Omniport function:

      Unbalanced instrument input



      500 Series module


      Durable powder coat

      Size: (W x H x L)

      5.3" x 1.6" x 6.7" (134mm x 40mm x 170mm)



      Shipping size: (W x H x L):

      6.7" x 1.9" x 9.1" ( 170mm x 48mm x 231mm)

      Shipping weight:



      For use in dry locations only between 5°C and 40°C


      Radial 3-year, transferable

      Specifications are subject to change without notice.

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